Unloading system for rotary compressor



Oct. 31, C. BLOOM UNLOADING SYSTEM FOR ROTARY COMPRESSOR Filed Dec. 10.1965 I 60 38 i z 7' Q 80 46 55 54 7i 50 56'. e 32-- s 4 02 G4-- 4a E:/j/66 68 w.\ K 20 fl. 4.3 g2 l2 \l6 0 2o 40 so I 80 '00 AIR DEMAND AS AOF FULL CAPACITY F! G. 2

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CA R L B LO 0 M United States Patent C) 3,349,994 UNLOADING SYSTEM FORROTARY COMPRESSOR Carl Bloom, Springfield, Mass, assignor to WorthingtonCorporation, Harrison, N.J., a corporation of Delaware Filed Dec. 10,1965, Ser. No. 512,895 11 Claims. (Cl. 23045) ABSTRACT OF THE DISCLOSUREAn unloading system for rotary compressors including a pumping deviceoperatively associated with the discharge of the compressor to rapidlyevacuate the compressor discharge during the unloading of thecompressor. This rapid evacuation of the compressor discharge materiallyand rapidly reduces the power consumption of the compressor.

This invention relates to a new and improved compressor unloading systemfor materially increasing the overall operational efficiencies ofcompressors by satisfactorily and materially reducing the powerconsumption thereof under all but fully loaded conditions.

On, for example, conventional rotary compressors of the prior art whichare equipped with large gas receivers in the nature of large air-oiltank means, compressor unloading is generally accomplished by closing ofthe compressor intake manifold and the concurrent bleeding of thecompressor discharge manifold and air-oil tank means to atmosphere, toresult in a large reduction of compressor power consumption. A primarydisadvantage of this procedure is the limited speed with which the saiddischarge manifold and air-oil tank means may be bled down withoutresulting in undesirable. oil foaming. Conversely, if lower rates ofbleed down are utilized to prevent oil foaming, the reduction incompression power consumption, and attendant increase in the overalloperational efiiciency of the compressor, are markedlyreduced,especially in applications wherein rapid and frequent cyclingofthe compressor between fully loaded and fully unloaded conditions isrequired.

It is, accordingly, a primary object of this invention to provide newand improved apparatus which will enable automatic and very rapidbleed-down of a compressor discharge manifold, concurrently withcompressor unloading, to result in very significant decreases incompressor power consumption at such times without giving rise toproblems in the nature of oil foaming.

Another object of this invention is to provide a means for reducing thepower consumption of a compressor by evacuating the discharge manifoldto a pressure well below atmospheric.

Another object of this invention is the provision of apparatus as abovewhich are particularly adaptable for use in materially increasing theoverall operational efliciencies of compressors which are required torapidly and frequently cycle between fully loaded and fully unloadedconditions.

Another object of this invention is the provision of apparatus as abovewhich also function to rapidly and automatically reduce the flow oflubricating oil to the compressor, concurrently with compressorunloading, to even further increase the overall operational efliciencyof the compressor.

A further object of this invention is the provision of apparatus asabove which require the use of only inexpensive and readily availablecomponents of well established design and proven dependability whereby,the-costs of fabrication and installation of the apparatus are minimized, and long periods of maintenance-free, satisfactory operationthereof assured.

3,349,994 Patented Oct. 31, 1967 The above and other objects andadvantages of my invention are believed made clear by the followingdetailed description thereof taken in conjunction with the accompanyingdrawings wherein:

FIGURE 1 is a schematic diagram of a rotary compressor whichincorporates the new and improved compressor unloading system of myinvention therein;

FIGURE 2 is a schematic diagram of a modified form of the oil controlvalve assembly of the system of FIG- URE l; and

FIGURE 3 is a graph of power plotted against capacity for a plurality ofrotary compressors, including one which utilizes the new and improvedunloading system of my invention.

Referring now to FIGURE 1, a rotary compressor system is generallyindicated at 10 and comprises a conventional rotary compressor 12 whichincludes a discharge manifold 14 and a compressor suction control asindicated generally at 16. An oil-air tank 18 is connected as shown tothe compressor discharge manifold 14 by a conduit 20 extendingtherebetween, and a check valve 22 of conventional construction, forexample of the swing check or disc type, is connected as shown in theconduit 20 to permit fluid How in the latter only in the direction fromthe compressor discharge manifold 14 to the oil-air tank 18.

A bypass conduit 24 extends as shown from the compressor dischargemanifold 14 to a portion of the conduit 20 downstream of the check valve22 to enable fluid flow from the said compressor discharge manifold tothe oil-air tank 18 around the said check valve. An auxiliary pump 26 isconnected in the bypass conduit 24 to enable the rapid evacuation of thecompressor discharge manifold 14 through the said bypass conduit. Theauxiliary pump 26 is designed to operate whenever the compressor 12 isoperating, whereby the former may conveniently be riven from the driveshaft of the latter as indicated schematically by the dashed line 27 inFIGURE 1.

A compressed air'supply conduit 28 extends as shown from the top of theoil-air tank 18, and includes a demister 30 connected therein as shownfor removing water and oil from the compressed air prior to theutilization thereof.

A lubricating oil supply line 32 extends from the bottom of the oil-airtank 18 to the rotary compressor 12, and includes oil filter means 34and oil cooler means 36 positioned therein as shown. A plunger operated,oil control valve 38, of generally conventional construction, is alsoincluded in the said oil supply line, and may be conveniently actuatedas shown by an extension 40 of the compressor suction control actuatingrod. The rotary compressor 12 and oil control valve 38 are designed sothat movement of the compressor suction control actuating rod 44 in thedirection indicated by arrow 42 will function to both unload the saidcompressor and partially close the oil control valve 38 to materiallyreduce the How of oil to the rotary compressor 12 through oil supplyline 32 during those times when the said compressor is operating underunloaded conditions.

Referring now to FIGURE 2, a modified form of con trol means for usewith rotary compressor assemblies which comprise suction unloaderpressure regulations is indicated generally at 41. In this case, theoperation of plunger operated, oil control valve 38 is controlled by thepressure signal fed to the compressor suction unloader actuator 43. Tothis efiect, the control means 41 comprise a housing 44 into which thevalve operating plunger 46 extends as shown. A diaphragm 48 extendsacross the interior of the housing 44 to divide the latter into chambers50 and 52, respectively, with the chamber 50 being vented to atmosphereby the clearance between the oil control valve actuating rod 46 and thehousing 44 as indicated at 54. A biasing spring 55 is positioned asshown 3 between the housing 44 and diaphragm 48 to bias the latter awayfrom the oil control valve 38.

The oil control valve actuating rod 46 is connected to the centralportion of the diaphragm 48, as indicated at 56, so as to be movabletherewith, and a conduit 58 extends as shown from the chamber 52 inhousing 44 to suction unloader pressure actuator 43, whereby pressuresignals from the latter may be readily communicated to the said chamberthrough the said control pressure conduit.

In the operation of the compressor assembly of FIGURE 1, the rotarycompressor 12 is unloaded by movement of the compressor suction controlactuating rod 40 in the direction indicated by arrow 42 to both closethe compressor suction control 16 to unload the compressor 12, andpartially close oil control valve 38 to materially reduce the fiow ofoil to the said compressor.

As this occurs, the pressure in compressor discharge manifold 14 fallsbelow the pressure of the compressed air in the oil-air tank 18, wherebythe check valve 22 closes to prevent reverse flow therebetween throughconduit 20. Concurrently therewith, operation of the auxiliary pump 26results in very rapid evacuation of the compressor discharge manifold 14through conduit 24 connected therebetween to very rapidly reduce thepressure in the said compressor discharge manifold to a value well belowatmospheric pressure.

This very rapid reduction in the pressure in the compressor dischargemanifold 14 and the very low pressure achieved in the discharge manifold14 reduces the power consumption of the rotary compressor 12, underunloaded conditions, to less than of the full load power consumption ofthe said rotary compressor. Thus it may be readily appreciated that thenew and improved compressor unloading system of my invention enablesvery rapid reduction in the discharge pressure of a rotary compressorconcurrently with the unloading thereof, with attendant significantincrease in overall compressor operation efiiciency; while preventingundesirable oil foaming, as discussed hereinabove due to the fact thatrapid bleed down of the oil-air tank 18 is rendered unnecessary in theunloading of the compressor.

Movement of the compressor suction control actuating rod 40 in thedirection indicated by arrow 42 to unload the rotary compressor 12, alsoresults in a partial closing of the oil control valve 38, as discussedabove, whereby the fiow of oil to the compressor through oil supplyconduit 32 is materially reduced to materially reduce the load on theauxiliary pump 26 and the power consumption of the compressor duringsuch time as the rotary compressor 12 is operating under unloadedconditions.

The oil control valve control means of FIGURE 2 operate to partiallyclose the oil control valve 38 concurrently with the unloading of therotary compressor 12 through the use of the same positive pressuresignal which is fed from the suction unloader actuator 43 to thecompressor suction control 16 to unload the said rotary compressor. Tothis effect, the said positive pressure signal is also fed from thesuction unloader actuator 43 to the chamber 52 in housing 44 throughconduit 58 connected therebetween. This results in an increase inpressure in the said chamber and attendant movement of the diaphragm 48and oil control valve actuating rod 46 toward the said oil control valveto partially close the latter and reduce the load on the auxiliary pump26 as discussed above.

The significant advantages, in addition to oil foaming prevention,provided by the new and improved compressor unloading system of myinvention, as compared to the compressor unloading systems which haveheretofore been utilized, are believed made clear by a comparison of thefollowing ratios of compressor power consumption under unloadedconditions to compressor power consumption under full load conditions at100 p.s.i. Thus, for standard compressor unloading systems utilizingmodulating control means, the said ratio has been determined by theactual taking of test data and subsequent calculations to beapproximately 0.63. The said ratio for compressor unloading systemswhich function through the bleeding of the compressor discharge manifoldto atmosphere has been similarly determined to be aproximately 0.20;while the said ratio for the new and improved compressor unloadingsystem of my invention has been similarly determined to range from ahigh of 0.15 to a low of 0.10, to thus make clear the significantadvantages provided by use of the latter. It is to be noted that theabove ratios are for steady state operation, and since the new andimproved compressor unloading system of my invention acts more quicklythan the system of bleeding the discharge manifold pressure ofatmosphere, the significantly reduced compressor power consumption is ineffect over a longer part of the unloaded portion of the load-unloadcycle. Thus, total compressor power consumption savings for the new andimproved compressor unloading system of my invention are therefore evengreater when the compressor is partially loaded than would be indicatedby the said ratios.

This is believed made clear by a comparison of the curves of FIGURE 3,wherein compressor power consumption as a percent of full load power isplotted against air demand as a percent of full load capacity. Curve 60represents the factors, as again determine-d by the actual taking oftest data and subsequent calculations, for a rotary compressor utilizinga standard unloading system of the modulating control type. Curve 62represents these factors, similarly calculated, for a rotary compressorutilizing an unloading system wherein the suction is either fully openor fully closed. Curve 64 represents these factors, similarlycalculated, for a rotary compressor utilizing an unloading systemwherein the suction is either fully open or fully closed, but whichbleeds the compressor discharge manifold pressure to atmosphere eachtime the suction is closed. Curve 66 represents these factors, similarlytaken, for a reciprocating compressor utilizing an unloading system ofthe constant speed type. Curve 68 represents these factors, similarlytaken, for a rotary compressor utilizing the new and improved compressorunloading system of my invention. With particular regard to curve 68, itis believed of interest to note that the rotary compressor requiresapproximately 12% of full load power while operating under unloaded orzero c.f.m. (cubic feet per minute) condltions, which is, of course,significantly lower than that provided by curves 60, 62, 64 and 66. Inaddition, curve 68 is believed to make clear, as discussed hereinabove,that compressor power consumption under partrally loaded conditions, asfor example in the 20% to capacity range, is significantly loweredthrough the use of the new and improved compressor unloading system ofmy invention.

While these have been shown and described herein, as the preferredembodiments of the invention, it will be understood that minor changesin the process and apparatus may be made without departing from thescope of the invention as disclosed and claimed. Thus, for example,although not at present preferred, the drive means for auxiliary pump 26may be modified, in any convenient manner, to effect the drive of thesaid auxiliary pump only upon operation of the compressor unloadingmeans to unload the compressor, rather than on the continuous basisdescribed hereinabove. In one form, this modification could encompassthe incorporation of non-illustrated clutch means through which the saidauxiliary pump is driven, with the said clutch means being engageableonly in response to the operation of the compressor unloading means tounload the compressor.

What is claimed is:

1. In a compressor system, a compressor having intake and dischargemeans, unloading means cooperatively associated with said compressor andoperable to unload said compressor, discharge conduit means and bypassmeans associated with said compressor discharge means, and pump meanshaving separate intake and discharge means, said pump intake meansconnected with said bypass conduit means, said pump means operable torapidly evacuate the said compressor discharge means whereby, the powerconsumption of said compressor may be rapidly and materially reduced byoperation of said pump means to rapidly evacuate said compressordischarge means concurrently with the operation of said compressorunloading means to unload said compressor.

2. In a compressor system as in claim 1 wherein, said pump means areoperable continuously with the operation of said compressor.

3. In a compressor system as in claim 1 further comprising, compressordrive means, and wherein said pump means are driven from said compressordrive means.

4. In a compressor system as in claim 1 further comprising, meanscooperatively associated with said compressor and said pump means forsupplying lubricating oil to said compressor, means for controlling theoperation of said lubricating oil supply means by controlling thequantity of lubricating oil supplied thereby to said compressor, meanscooperatively associated with said compressor unloading means and saidlubricating oil supply control means and operable to cause the latter toreduce the amount of lubricating oil supplied to said compressor inresponse to operation of said compressor unloading means to unload saidcompressor whereby, the load on said pump means is reduced concurrentlywith the unloading of said compressor.

5. In a compressor system as in claim 4 wherein, said pump means areoperable continuously with the operation of said compressor.

'6. In a compressor system as in claim 4 wherein, said meanscooperatively associated with said compressor un loading means :and saidlubricating oil supply control means comprise, a compressor unloadingmeans actuating rod extending therebetween.

7. In a compressor system as in claim 4 wherein, said meanscooperatively associated with said compressor unloading means and saidlubricating -oil supply control means comprise, pneumatically operablemeans connected to the latter and means for communicating pressuresignals from said compressor unloading means to said pneumaticallyoperable means.

8. In a compressor system, a rotary compressor having an intake manifoldand a discharge manifold, unloading means cooperatively associated withsaid intake manifold and operable to unload said compressor, dischargeconduit means extending from said discharge manifold, check valve meansin said discharge conduit means for preventing fluid flow therein in thedirection toward said discharge manifold, bypass conduit meansconnecting said discharge manifold with a portion of said dischargeconduit means downstream of said check valve means, pump means in saidbypass conduit means for pumping fluid from said discharge manifold tosaid portion of said discharge conduit means, said pump means beingoperable to rapidly evacuate said discharge manifold whereby, the powerconsumption of said compressor may be rapidly and materially reduced byoperation of said pump means to rapidly evacuate said discharge manifoldconcurrently with the operation of said compressor unloading means tounload said compressor, and flow of fluid into said discharge manifoldthrough said discharge conduit means prevented by operation of saidcheck valve means.

9. In a compressor system as in claim 8 wherein, said pump means areoperable continuously with the operation of said compressor.

10. In a compressor system as in claim 8 further comprising, air-oiltank means connected to said discharge conduit means downstream of saidportion of the latter, cond-uit means connecting said air-oil tank meansand said compressor for supplying lubricating oil from said airoil tankmeans to said compressor, valve means in said conduit means forcontrolling the quantity of lubricating oil supplied therethrough tosaid compressor, and means cooperatively associated with said valvemeans and said compressor unloading means and operable to cause saidvalve means to reduce the amount of lubricating oil supplied to saidcompressor in response to operation of said compressor unloading meansto unload said compressor whereby, the load of said pump means isreduced concurrently with the unloading of said compressor.

11. In a compressor system as in claim 10 wherein, said pump means :areoperable continuously with the operation of said compressor.

References Cited UNITED STATES PATENTS 1,616,992 2/ 1927 Ruckstuhl230-27 1,716,160 6/ 1929 Zworyskin et a1. 230-45 2,492,075 12/1949VanAtca 230-45 2,826,353 3/1958 Auwarter et a1 230-45 2,914,242 11/1959Meien-berg 230-45 2,958,455 1/1960 Steinherz et a1. 230-45 2,971,6912/1961 Lorenz 230-45 3,101,187 8/1963 Campbell 230-27 3,110,473 11/1963Frank et al. 253-3915 3,147,712 9/1964 Gaubatz 103-5 3,191,854 6/1965Lowler et a1. 230-24 DONL'EY J. STOCKING, Primary Examiner. W. I.KRAUSS, Assistant Examiner.

1. IN A COMPRESSOR SYSTEM, A COMPRESSOR HAVING INTAKE AND DISCAHRGEMEANS, UNLOADING MEANS COOPERATIVELY ASSOCIATED WITH SAID COMPRESSOR ANDOPERABLE TO UNLOAD SAID COMPRESSOR, DISCHARGE CONDUIT MEANS AND BYPASSMEANS ASSOCATIED WITH SAID COMPRESSOR DISCHARGE MEANS, AND PUMP MEANSHAVING SEPARATE INTAKE AND DISCHARGE MEANS, SAID PUMP INTAKE MEANSCONNECTED WITH SAID BYPASS CONDUIT MEANS, SAID PUMP MEANS OPERABLE TORAPIDLY EVACUATE THE SAID COMPRESSOR DISCHARGE MEANS